1. Field of the Invention
The invention generally relates to a cycle piston engine power system and more particularly to a semi-closed cycle piston engine power system having an integrated oxygen generation, SC CO2 heat recovery and carbon dioxide capture and clean-up sub-systems.
2. Background of the Related Art
Conventional power systems, whether internal or external combustion, burn fuel with air and generally vent the combustion products (exhaust/flue gas) to the air (or via underwater interface to the air). This is true of natural gas, gasoline, and diesel piston engines, and also of gas turbines, jet engines, or even steam boiler based power plants. Emissions of the untreated flue gas to the air, while simple to execute, is not desirable for environmental reasons. Gases such as SO2, NOx, CO, HC (unburned hydro carbon) and more recently CO2 are defined as pollutants and are regulated. In special purpose applications, in particular for undersea applications, the requirement to tie the system exhaust pressure to the ambient pressure (elevated backpressure) can lower engine cycle efficiency significantly. In other special purpose applications, in particular at higher altitudes, the requirement to tie the system pressure to the ambient pressure (reduced inlet pressure) can reduce specific power significantly, and may also impact efficiency.
As a result, there has been a desire to become non-emissive and/or to have less of an adverse impact from the local ambient pressure, and prior work on various closed or semi-closed power systems has occurred. Historically (in the first part of the 1900's) this work was mostly related to the special purpose applications. More recently it is mostly about the ability to provide higher efficiency and/or effectively control emissions or even capture system emissions, in particular CO2.
The strongest early motivation to develop closed and semi-closed power systems has been tied to the production of power undersea. In U.S. Pat. No. 2,884,912, a simple method of operating a piston engine using liquid oxygen, while using the liquid heat of vaporization to condense the products is disclosed. Since this is an undersea application, there is no discussion of product clean up or the production of oxygen. In U.S. Pat. No. 3,134,228 another clearly undersea semi-closed power system is disclosed, using turbines. Again, liquid oxygen (LOX) is carried on board as the oxidizer. Condensed water is pumped and used as the combustion diluent to control temperatures, in the same way water, oxygen, and hydrocarbon are combined in “steamfish” torpedoes, such as the US Mk 16 (introduced late in WWII). In U.S. Pat. No. 3,559,402, liquefaction of the CO2 and storage is disclosed. Again the vaporization of the onboard liquid oxygen is used to provide the refrigeration. Importantly, no effort is made to operate the engine at other than normal atmospheric conditions. In fact, 14 psia is the recirculating pressure for the CO2/O2 stream.
In U.S. Pat. No. 3,736,745, a “supercritical” closed cycle turbine system is introduced. There are some technical problems with this patent, but it is intended to operate at depth and at high enough backpressure that both the CO2 and water product are condensed together as liquids, without the use of cryogenic oxygen.
In U.S. Pat. No. 3,980,064, Nissan motors provides details on a piston engine or rotary piston engine patent using H2O2 as the oxidizer. This system includes exhaust recirculation, but the patent is mostly about the injector design and the ability to burn multiple fuels. Injector design for direct use of H2O2 is critical as decomposition can occur at points in the cycle where it would not be desirable.
In U.S. Pat No. 4,434,613, the General Electric Company introduces the semi-closed cycle gas turbine (Brayton Cycle) for “chemical” production, including CO2. This patent is clearly not for undersea application, and the integration of the system with a cryogenic air separation unit is included. The system is not operated at high backpressure, and the recirculated exhaust gases (O2, CO2 and others, not mentioned herein). The point of this gas mixture is to mimic the thermodynamic properties of air, so that existing, 14 psia inlet pressure molecular weight 29 (air) gas turbine machinery designs could be used. As is also typical of GE, a Heat Recovery Steam Generator (HRSG) is used, not a recuperator. However, U.S. Pat. No. 3,134,228, does not disclose any details or methodologies associated with product gas clean up. In U.S. Pat. No. 4,674,463, the Cosworth Engine company reintroduces the semi-closed cycle piston engine for undersea applications. The ability to vary the oxygen concentration to values lower than 21% was used to limit oxygen loss in the direct sea water condensation process.
In the Dunn Brayton Patents, U.S. Pat. Nos. 7,926,275, 7,926,276, 7,937,930, 7,951,339, and 8,156,726, the closed (metal fuel) and semi-closed (hydro carbon fuel) Brayton (gas turbine) cycles are introduced. These patents are specifically not at atmospheric pressure, but at high closed cycle pressures (subcritical or supercritical). Inert gas working fluids, mixtures of inert gas working fluids and CO2, and CO2 only are discussed. Two of these patents address a gas clean up methodology, but it is not associated with gas product, but with scrubbing any metal vapor (fuel) out of the gas to avoid plating inside the turbine or recuperator. Oxygen generation is not addressed, since these patents were targeted towards undersea systems with high pressure bottled or liquid oxygen.
In U.S. Pat. No. 8,205,455, GE provides a complex arrangement of gas turbines, with stoichiometric (air based) combustion and exhaust gas recirculation. In this system, N2 and CO2 are recirculated, and only enough high pressure air is used to support the combustion—the reduction in excess air makes the flue gas easier to clean up for other applications.